A metric for the efficiency of light emitting diodes (LEDs) is the luminance per watt. The luminance provided by light emitting diodes is dependent upon several factors, such as internal quantum efficiency, which quantifies the fraction of injected carriers converted to photons, or extraction efficiency, which quantifies the fraction of photons successfully extracted from the light emitting diode. Internal absorption may prevent photons from escaping the light emitting diode. To realize high efficiency LEDs, both the internal efficiency and extraction efficiency should be addressed. The potential gains from improving extraction efficiency, however, are likely to be greater and simpler to accomplish than the gains from improving internal efficiency.
From the above, it is seen that improved techniques for manufacturing optical devices are highly desired.